1. Field of the Invention
The present invention relates to a power disconnection apparatus, especially to a power disconnection apparatus for soft-shell Li ion battery.
2. Description of Prior Art
High-capacity battery becomes increasingly important as the prevailing of mobile electronic device. More particularly, lithium ion (Li-ion) battery using lithium transition metal as anode and carbon material as cathode is under extensive research.
However, the Li-ion battery is subjected to an over-charge problem when excessive Li ion is extracted from anode and lithium metal is precipitated due to insertion of Li ion at cathode. Unstable peroxide is generated at anode, which loses lithium ion. The organic solvent in the electrolyte has decomposition reaction when the over-charge voltage is above a voltage threshold. Moreover, lots of flammable gas is also generated. The battery has abnormal heating due to rush heat generation, which induces risk of battery damage.
The applicant of the subject application has proposed various protective mechanisms for charging battery, for example, Taiwan Utility Model TWM292169 and TWM275625. More particularly, Taiwan Utility Model TWM292169 discloses a protection apparatus for Li-ion battery. The protection apparatus for Li-ion battery comprises an abnormality detection circuit and a photo-coupling circuit. The abnormality detection circuit examines the voltage of the rechargeable battery and outputs a detection signal. The photo-coupling circuit is electrically connected to the abnormality detection circuit and adjusts an impedance thereof according to the detection signal output from the abnormality detection circuit. The connection between the rechargeable battery and an external circuit is opened or close for discharging or charging the rechargeable battery. The Taiwan Utility Model TWM275625 also discloses a protection apparatus for rechargeable battery. The protection apparatus for rechargeable battery mainly comprises a first protection loop and a second protection loop. The first protection loop comprises a main current load connected to a main circuit and a battery, and a thermo-coupler switch connected to the battery and the main circuit. The second protection loop comprises a protection circuit and a heater. The protection circuit is connected to the main circuit and senses the battery voltage for generating a start signal. The heater is connected to the protection circuit and is activated by the thermo coupler switch. Moreover, the mechanical protection apparatus for cylindrical hard-shell Li ion battery activates a blow-off valve when the internal pressure is increased due to excessive charging of batter. A conductive pin is broken by the operation of the blow-off valve to provide protection.
The above-mentioned protection mechanism for Li ion battery can provide limited protection for over-charged Li ion battery. However, the above-mentioned protection mechanism has risk of damaging components of battery after long time use. The mechanical protection mechanism for the cylindrical hard-shell Li ion battery cannot be used for soft-shell Li ion battery. Moreover, the above-mentioned protection mechanism has complicated components. It is desirable to provide a protection mechanism for Li ion battery with simple structure and with no harm to the components of the Li ion battery.